1. Field of the Invention
The present invention relates to an endoscope system using normal light and fluorescence for obtaining normal reflected light images and fluorescent images.
2. Description of the Related Art
Endoscopes are widely used today in the medical field and the industrial field. Particularly in the medical field, a technology to obtain images which make it easier to identify normal tissue and abnormal tissue has been proposed, in addition to an endoscope system for obtaining normal-light images using conventional white light.
For example, as a first prior art, Japanese Patent Laid-Open Publication No. 2001-137174 discloses a system for generating display signals mainly by reflecting the relative intensity of fluorescence to the color, and the intensity of a reference light to the luminance.
As a second prior art, Japanese Patent Laid-Open Publication No. 2000-270265 discloses a system for overlaying fluorescent images and background images.
As a third prior art, Japanese Patent Publication No. 5-37650 discloses a system for detecting an abnormal section of the respiratory metabolism of a human body using fluorescent images and reference images by reference light.
As a fourth prior art, Japanese Laid-Open Publication No. 10-309282 discloses a system for irradiating excitation light and obtaining images which make it easier to identify normal tissue and abnormal tissue by two fluorescent images with different wavelength bands and reflected images by excitation light.
In addition to these, the following are also prior art.    (a) U.S. Pat. No. 5,827,190
This patent discloses a system for creating fluorescent images and non-fluorescent images. Excitation light (400 to 450 nm) and illumination light (including 700 nm) are sequentially irradiated endoscopically, and fluorescent and reflected light generated from biological tissue are received by an image pickup device. These signals are displayed on a monitor such that pathologically affected tissue and normal tissue can be distinguished.
Or, the irradiation time of the above mentioned excitation light is set to longer than that of non-excitation light (illumination light). By building a CCD into the tip of the endoscope and by integrating the pixels of the CCD when fluorescent images are captured (when excitation light is irradiated), brightness (S/N) is improved.    (b) Japanese Patent Laid-Open Publication No. 10-151104
This patent discloses a system for sequentially displaying conventional-light images and fluorescent (infrared) images. A rotary filter for conventional-light images and a rotary filter for fluorescent images are arranged concentrically, and the rotary filters move depending on the mode (FIG. 12 to FIG. 17 of this gazette).
Also an optical aperture for transmitting the infrared light is installed at the tip of the endoscope, so in fluorescent mode, brightness can be improved since more infrared light transmits. With visible light, the opening (see FIG. 6 of this gazette) is restricted by the optical aperture, so ability of distinction becomes high.    (c) Japanese Patent Laid-Open Publication No. 10-201707
This patent discloses a system for sequentially displaying normal-light images and fluorescent images. It is disclosed that the filter which transmits the visible light and the filter which transmits the infrared light are selected by switching the mode (normal-light images and fluorescent images) for the rotary filters red and infrared, G and B, installed at the light source (FIG. 9 to FIG. 11 of this gazette).
In the first prior art, the intensity of the fluorescence emitted from a normal tissue differs depending on the patient, so the color tone of a normal tissue differs depending on the patient, and the identification of pathologically affected tissue and normal tissue may be difficult in some cases.
In the second prior art, reflected light has a wide band, so the function to obtain images, which make it easier to identify normal tissue and pathologically affected tissue, drops.
In the third prior art, a regression line to the target tissue is derived using the fluorescent images and reference images, but only the wavelengths of the reference images are matched with the wavelengths of the fluorescent images, so the identification function between the normal tissue and pathologically affected tissue may not be sufficiently performed.
The fourth prior art has a complicated configuration.